


Playing with Fire

by Mirako12



Series: Todomomo/Royai FMA AU [1]
Category: Fullmetal Alchemist: Brotherhood & Manga, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: Alchemy, Alternate Universe, Crossover, Eventual Romance, F/M, Flame Alchemy, Fuhrer Roy Mustang, Parental!Royai, Slow Burn
Language: English
Status: In-Progress
Published: 2018-12-22
Updated: 2019-06-16
Packaged: 2019-09-25 01:34:11
Rating: Not Rated
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,344
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17111939
Author URL: https://archiveofourown.org/users/Mirako12/pseuds/Mirako12
Summary: There can be no more flame alchemists.When their daughter Momo shows much promise as an alchemist, Roy and Riza Mustang resolve to keep flame alchemy from her in hopes that their secrets will die with them. However, the appearance of a mysterious red-and-white-haired boy leads to an unsettling realization: the fire may be well beyond their control.(Aka the Todomomo/Royai crossover nobody asked for but I felt compelled to write.)





	1. Chapter 1

**Summary for the Chapter:**

> As the daughter of the famed Flame Alchemist and Hawk's Eye, she knew the dangers of attempting Flame Alchemy. There's something about Shouto that makes her think differently, though, so the two of them decide to try it anyways.
> 
> UPDATE: So this chapter was the original concept piece before I decided to make this a multi-chapter fic. Consider this an excerpt if anything? There's nothing particularly spoiler-y that the summary doesn't already imply.

“You know how to snap, don’t you?” She asks the boy standing in front of her as he carefully pulls on white gloves with familiar-looking red markings. Momo supposes she should feel guilty for stealing a pair of them from her father. He _is_ the Fuhrer, after all. But he is more doting father than Fuhrer to her so she figures she can probably get away with it.

 

Just like she’s gotten away with all these late nights spent with _him_.

 

“Of course,” he says, looking over his shoulder.  Her heart jumps as his eyes meet hers but she still smirks back in reply.

 

_Shouto Todoroki._

 

Soldiers in the North had found him buried in the snow near Fort Briggs. Once her father had learned from General Olivier Armstrong that he was just a kid and didn’t have anyone to look after him, he had insisted on taking him in despite all warnings and precautions. Fuhrer Roy Mustang had, after all, been orphaned at a young age. He couldn’t help but empathize with those who had lost their parents.

 

That was more or less how the boy had found himself a semi-permanent guest at the Mustang residence in Central. Momo was exceedingly grateful for his presence—there was no one else her age on the premises. He had made the last couple months of her life so much more _exciting_ . She wasn’t sure if it was necessarily _him_ that made it so, or just the newness of it all.

 

She had always thought Uncle Edward and Alphonse were unique with their golden hair and golden eyes, shining bright as the sun—trademarks of the ancient civilization of Xerxes. Never has she encountered anyone with hair as pale as the moon. Or beautifully bright red—the same red as the philosopher stone that restored her father’s sight—or so she’s been told.

 

Let alone _both colors simultaneously_. There has never been any accounts of anyone with dual-colored hair split halfway down the middle, as far as she knows. That in itself is quite the curiosity.

 

And his eyes— _Heterochromia_. It’s something she’d read about in books but had never seen for herself before him. She remembers the first time she looked into his eyes—one stormy grey, the other a brilliant turquoise—and how she thought she’d never seen anything so curious—or beautiful—in her life.

 

Within the first month of his stay, they discovered he had an affinity for ice alchemy. She herself had been nicknamed the fledgling Creation Alchemist by the general public due to her wide knowledge of formulas and complex transmutations. But not of the same magnitude as his.

 

That day was one of the few times her mother hadn’t been at her father’s side out in public. The crowd had made it hard to see much of anything. It had all happened so quickly. The man who had attempted to assassinate Fuhrer Mustang had been in reach of his goal—and suddenly stopped in his tracks.

 

It took a moment for them to realize Shouto had grabbed his arm and frozen him solid.

 

It didn’t look like he had even used a transmutation circle.

 

* * *

 

Something about the boy makes her think he’d be a prodigy at this as well. He is everything she’s not in terms of raw power and ability. Momo wants to believe that she, too, can learn to use flame alchemy—her father is _the_ Flame Alchemist of the past, after all—but the countless hours spent with Shouto poring over alchemical texts has proven that he just seems to intuitively _get_ these things. She can’t help but wonder if it has anything to do with the curious color of his hair—white for ice and red for fire? But there is no logical reason that should be the case.

 

“Okay…” she takes a deep breath, training her eyes on the candlestick she had placed a few feet in front of them. They had done their best to clear away anything flammable. In retrospect it probably would have been best to try this somewhere outside, but they’d run a higher risk of getting caught. That and the heavy drumming of rain on the window confirms that the environment would not be conducive to their activities at this moment.

 

“...try to concentrate the oxygen into a narrow stream leading to the candle wick,” she says, double checking the notes in the leather-bound book she is holding. “All you need is a spark to start the reaction.”

 

“Got it.” He straightens his stance as she looks on. She can’t help but notice the heroic way his chest puffs out, head held high and arm outstretched, eyes fixated on the candle. The look of determination he has reminds her vaguely of a certain photo she’s seen of her father; the one taken when he was promoted to General. It’s one of the few photos her parents have together from their younger days. Her mother was still dutifully following behind him even back then, always watching his back.

 

She also can’t help but think there’s congruity in their own positions right now; her watching his back as they attempt this.

 

He snaps.

 

A burst of flames engulf the space in front of them and Momo yelps in surprise. They both jump back, Shouto instinctively raising an arm up to shield her. His head whips around to look at hers.

 

“Are you okay?”

 

Her shoulder burns from where his hand had gently brushed against her skin. His concern has brought his face dangerously close to hers. The room feels warmer, probably due to the flames he had just created. She nods.

 

“I’m fine.”

 

She didn't mean to lean in, but somehow their foreheads are almost touching. It feels a bit harder to breathe—maybe he had used up a bit too much oxygen in that transmutation. His face is red, too, and there’s beads of sweat dripping off his brow. The scar on the left side of his face seems brighter, and without thinking she reaches up to touch it, gently brushing aside some of the bangs covering his turquoise eye.

 

He lets her.

 

 

 

It occurs to her that it smells like something is burning.

 

She pulls her attention away from him to assess the space in front of them and he does the same. Momo chides herself for getting distracted from doing this first—they very well could have burned the entire building down with their recklessness.

 

Luckily, there’s no obvious damage, _and_ despite the initial ferocity of the flame he had created…

 

...the candle is lit, small flame flickering but burning all the same.

 

_It worked._

 

“You’re amazing, Shouto,” she breathes in awe, looking up into his eyes.

 

The smile he gives her could have melted all the snow in the North.

 

* * *

 

Momo leaves that night with a skip in her step and a strange feeling in the pit of her stomach. Perhaps it was the look he gave her just before they had parted ways. Or maybe it’s guilt over what she and Shouto had just done. Her parents had always warned her about the destructive power of fire, after all.

 

She knew better than to be playing with it.

**Notes for the Chapter:**

> Short concept piece for now, but this was the other multi-chapter fic idea I had. Royai is my OTP of OTPs and Todomomo is currently a close second so I thought it'd be cool to tie the two together. I have _so many ideas for where to go with this asdfjkl;_
> 
> Somewhat inspired by that one post saying Momo looks like she could be Roy and Riza's child? XD
> 
> And yes, the photo she's referring to is the infamous mustache pic from the FMAB epilogue (or the corresponding manga pic~you decide)


	2. Man of Many Names

**Summary for the Chapter:**

> Roy Mustang has had many titles over the course of his life, but is especially excited about his latest one: _Father_

_Fuhrer Roy Mustang._

 

He still hasn’t gotten completely used to it—just like he hasn’t gotten used to calling Hawkeye “Riza” even though they’ve been married for nearly three years now.

 

The title is a heavy burden to bear and sometimes he misses when he was just a Colonel.

 

Or even just Roy.

 

Roy-boy.

 

Those were simpler times.

 

_Flame Alchemist, Fuhrer, and soon-to-be Father._

 

He and Riza had not planned on having a child. While the desire for such a thing had come up far before they were officially married, they had both agreed that running the country and righting the wrongs of the past would be a full-time job with little room for much else, let alone the time investment required of _children_.

 

But then again, they _had_ spent countless nights making up for lost time, so perhaps he shouldn’t have been surprised when Riza found out she was pregnant.

 

The prospect of having a child is both exciting and terrifying.

 

He can tell Riza’s appreciation slowly turns to annoyance with how carefully he treads around her, how cautious he is as if she and their unborn baby are made of glass.

 

And of course he knows—he _knows_ Riza is tough as nails and their child, being their child, must be too—but somewhere in the back of his mind the law of equivalent exchange and the devilish grin of a ghostly figure sitting by his Gate continues to haunt his innermost thoughts. There’s an unspoken fear in his heart that Truth could very well take their child from them.

 

Or Riza.

 

Or _both_.

 

Thus, Roy is wholly relieved when their daughter is born perfectly healthy and his wife, though understandably winded, is practically glowing as she holds their child against her chest.

 

He’s not naive enough to think he deserves this.

 

And as he looks at the bundle in his wife’s arms—a beautiful baby girl with wide eyes, tiny hands balled into fists as she peers up at the two of them—he can’t help but tear up as he wonders how the world could be so merciful on the two of them after all they’ve done.

The Elric brothers had sought to prove that equivalent exchange wasn’t always equivalent—that by giving something, sometimes you received more back in return.

 

Maybe this was one of those cases.

 

_“Roy, do you want to hold her?”_

 

The sound of Riza’s voice tears him away from his thoughts. He realizes he’s been hovering above them, speechless, staring down with watery eyes. Roy half expects his wife to make some joke about how water never fails to make him useless. She doesn’t though, attention focused entirely on their newborn daughter.

 

His breath catches in his throat as he wordlessly takes the bundle from her arms and brings their daughter closer to his chest. Onyx eyes that reflect his own blink back at him as she coos quietly into the air between them. Roy brings one hand up to her face and watches as tiny fingers attempt to grasp at his thumb.

 

“She’s beautiful,” he murmurs, lowering himself to Riza’s level so they both can bask in the presence of the life they created, together.

 

“Of course she is,” his wife whispers back, bringing a hand up to cradle the back of her head.

 

Roy chuckles. “Sure doesn’t look like a Maes.”

 

“No,” Riza responds distractedly as she brings her face closer and lovingly strokes the crown of their daughter’s head, smiling. “I don’t think she does…”

 

They would have named her Maes, if she were a boy. Roy looks skyward, silently promising Maes that if they were so fortunate to have a son one day, he would definitely be named after the most loyal friend anyone could ask for.

 

Instead, they name her Momo.

 

* * *

 

Truth is not kind to everyone, as it would seem.

 

The Emperor of Xing has not been blessed with a child, and while Roy is on another routine visit to discuss the expansion of trade routes between Amestris and Xing, Ling himself postulates that such a blessing may never be.

 

This is after all their talk of business and Roy not-so-subtly gushing about Momo, who had just laughed for the first time a few days before he left for Xing. He and Riza had had a casual competition to see who could make her laugh first, and in the end it had been Black Hayate chasing his tail that had won a fit of giggles.

 

“What makes you so sure?” Roy inquires of Ling quietly, knowing full well that the Emperor’s ever loyal bodyguard is likely within earshot.

 

“There’s no way to know _for sure_ , but I suspect my time as a homunculus is the reason,” Ling states in a low voice. Roy ponders that thought, which unfortunately makes too much sense. Fuhrer King Bradley had stated the same—it is, perhaps the price to pay for immortality.

 

Ling has been doing his best to reform the hierarchy of Xing, but being Fuhrer himself has made Roy fully aware that country-wide changes are a process that never happens quickly. While the different clans no longer have to fight for the throne, the failure of the emperor to produce any heir at all does not bode well for the future.

 

He’s heard Alphonse and May are expecting a child somewhat soon, but Ling had shared that many clans have already expressed a distaste in the princess’s decision to marry someone of non-Xingese descent. It’s implied that many would be less than happy about the prospect of a half-Xingese half-Amestrian ruler as well.

 

“Then what about...” Roy finally catches a glimpse of a familiar figure in black, red and white mask camouflaged between the chinks of one of many ornately patterned window lattices.

 

_What about her?_

 

He recalls, years ago, Ling quietly stating his intention to marry the girl once things settled down. The emperor is quite a few years younger than him, and Roy had always accounted his decision to push off marriage to his preoccupation with the duties of being ruler of Xing. He never expected there were other factors at play. Now that he and Riza have been married for awhile, he can’t even imagine what life would’ve been like if circumstances had kept them from being together—or having their precious daughter.

 

The figure disappears as Ling comes to stand by him, glancing at the spot where she was before turning to Roy.

 

“Lan Fan remains my most trusted companion and loyal bodyguard,” he responds matter-of-factly. He turns away from Roy as he continues, hands clasped behind his back.

 

“The duty of an emperor’s wife is to bear children…” He sighs, shoulders sinking a bit deeper. He lowers his voice to utter the rest.

 

“I won’t have her take the blame for the choices I made.”

 

* * *

 

Momo quickly reveals herself to be quite the prodigy. She _loves_ books from a very young age. Roy has to admit—it gets a little tedious reading the same fairy tales to her night after night, but the starry-eyed look his daughter gets as she marvels at his story-telling voice makes it all worth it. With Roy busy during the day with meetings and other duties to attend to, bedtime stories quickly become a favorite father-daughter pasttime of theirs. By the time she turns four, she’s practically memorized her favorite stories to the point she can recite them back to him word-for-word.

 

On her fifth birthday, they hold a larger than usual party—Havoc jokes that he must have invited half of Amestris with how crowded the place is.

 

It _is_ fairly unusual for the Mustang residence to be this crowded these days. This current hum of conversation is comforting, though. Roy surveys the room, grateful for all the people who have played an important role in their lives. Of course, there are some people missing—he wouldn’t expect their friends from Xing to make such a long trek out, and while she had been invited, he’s not sure that General Olivier Mira Armstrong would consider him enough of a friend to travel to Central for a mere social event like this. And then of course, there are those who are no longer around…

 

Out of the corner of his eye, he sees their little guest of honor making a beeline towards him with a familiar-looking teen in tow. She comes screeching to a halt next to him, tugging incessantly on his arm.

 

“ _Dad, Dad!_ Are you going to light the candles this year?” She looks up at him with excited eyes and he lowers himself to put a hand on her shoulder and ruffle her ponytail of raven black hair. Momo bounces with anticipation. Her current expression never fails to melt his heart.

 

Riza had discouraged him from engaging in the tradition what with the larger than usual crowd, but… _how could anyone say no to that face?_

 

“Of course, sweetheart,” he reassures her, planting a quick kiss on her forehead. “Anything for my little girl.”

 

“Yay!” She turns back to her partner-in-crime. “See—I told you, Elicia! This year you’ll get to see it for sure! I bet you’ve never seen anything like it!”

 

“Ooh, really? I’m so excited!” She giggles in response before flashing him a knowing glance—after all, Momo wouldn’t know that he used to do the exact same thing for _her_ birthday when she was around the same age.

 

“Come on! Let’s ask Mom if we can eat the cake soon!” Momo jumps up and tugs on Elicia’s arm to relocate them to another area of the party. Roy grins amusedly.

 

“See you, Uncle Roy!” Elicia grins back at him as she follows after the now five-year-old. For a moment, Roy is reminded of Maes—she looks so much like him when she smiles like that. If only he were still around to see what a beautiful young lady his daughter had grown into. She is kind and compassionate and graceful like her mother, and retains the same youthful enthusiasm and optimism Maes had. He’s also heard rumors via Gracia that there have already been _several_ boys seeking her affection…and she’d gently turned them all down.

 

Maes would be proud. Well, maybe not about the last part…

 

Riza makes an appearance a few minutes later and motions him to come over to the table.

 

He pulls on his gloves, which are a much cleaner white than what they used to be. He hasn’t needed to use them in awhile, after all. Now that he’s Fuhrer, utilizing flame alchemy has been reduced to parlor tricks like these. It’s for the best, really. There’s no need for explosive fire alchemy these days, especially during this period of relative peace.

 

A familiar snap and the candles come to life. Sounds of awe echo among the birthday crowd. Roy catches Momo beaming at the gently flickering flames as everyone starts to sing. Her gaze darts over to the gloves on his hands before she turns her attention back to the candles in front of her. She closes her eyes to make a wish, but not before he catches a glimpse of something he’s seen before.

 

There is fire in those eyes.

 

* * *

 

It would be nice if all days were as carefree as those, but being Fuhrer comes with more than its fair share of challenges. Rebuilding Ishval was no easy task, and while things are mostly moving along it seems like every time he thinks everything is finally going well, they hit another setback. While there is widespread support of the current movement to reform the entire political structure of Amestris, there are a handful of groups who are harshly opposed to them—and the Fuhrer behind them all as a result.

 

Brigadier General Miles and Scar have been leading the restoration efforts and he’s been doing his best to meet with them routinely—because above everything else he has to do as Fuhrer, this was always the most important.

 

This particular meeting it’s just Scar. Roy listens intently as the man lists off the latest in skirmishes between the Amestrians and Ishvalans along the southeast border, and his own thoughts on the opposition they are currently facing.

 

“It is in our culture to forgive—to stop the cycle of hatred,” he explains. “But Amestris inflicted a lifetime of pain and suffering on us that for many, is impossible to forget.” He shakes his head as he turns to look to Roy. “It is a personal decision to forgive, and there are some who still hate you for the things you’ve done as the so-called Hero of Ishval.”

 

_Hero_.

 

The word burns in his memory every time he hears it.

 

There is nothing heroic about anything he did during the Ishvalan Civil War. Hero of Ishval is one title he’d like to forget.

 

“And what about you? Do you still hate me for the things I’ve done?” He looks back at the man who had tried to take his life—on several occasions—so many years ago.

 

Scar seems to ponder this for awhile. The fact they’ve been working together for the last few years indicate the opposite, but Roy mentally prepares himself for whatever his response may be. He _deserves_ to be hated for what he did, and even with everything he’s doing now to atone for the past—it will never be enough. It _shouldn’t_ be. It would be arrogant for him to believe _anything_ he does now can make up for the past— _but he still has to try, damn it._

 

“Hate is too strong a word now. I hated you, once,” Scar replies, calmly. “I don’t know that I can ever forgive you for what you did to my people.” He rises and walks over to stand by Roy, peering out the window at the expanse of desert before them, restoration efforts underway. “But I can see that the path you’ve chosen to take now is ultimately for our good, and for that reason I will continue to support you in your efforts.”

 

Roy glances over at him, relieved. “Thank you for that, Scar. I can only hope that the changes we’re making now will make things better for the next generation.”

 

Scar closes his eyes, seemingly deep in thought. “It’s pointless to cling to the dead, instead we need to fight to keep more from dying,” he says, slowly. “That’s something General Armstrong has said a number of times. While I don’t know if I can agree with her completely, there is truth to that statement.” He crosses his arms as he looks back out at the view before them. “Right now, looking to protect the future is more important than dwelling on the past.”

 

Roy nods in response. He allows the silence to settle between them briefly before he speaks up again.

 

“How is General Armstrong doing, anyway?” Roy smirks, crossing his arms. “Between you and Brigadier General Miles…it seems she sends one of you down to Central anytime her presence is requested these days. What, she can’t handle the heat?”

 

Scar tilts his head to the side. “I believe the General said she’d rather not see your stupid face if she doesn’t have to.”

 

Roy coughs. “Is that a direct quote?”

 

Scar shakes his head. “No. I don’t think you want to hear what she actually said.”

 

He sighs. “Fair enough.”

 

Some things never change.

 

* * *

 

It’s not long before Momo’s fascination with fairy tales soon turn to science and history. Many a night he and Riza had found their daughter asleep atop a pile of books with her lights still on. It’s always a plethora of volumes much thicker and more complex than what what Roy thinks a six-year-old can comprehend, and he can’t help but be amused that he can always pick out the slim volume of a fantasy novel hidden amongst the sea of information.

 

She had a fascination with the world beyond Amestris, so Roy had made it a point to give her all sorts of history books. She reads it all—Xing, Creta, Aerogo…

 

When she is seven, she transmutes something for the first time. It’s a Drachman nesting doll, mirroring the picture of one she’d seen in one of her history books.

 

Roy is _elated_. Their daughter has potential as an alchemist. There is so much he wants to share with her, so much that he can teach her—

 

—and he _does_ , giving her his old notes, gifting her alchemical texts for her birthday, collaborating on transmutation circles in the courtyard between his duties as Fuhrer. She soaks it all up, and _fast—_ much faster than he had when he was her age. He can’t help but beam with pride at what a beautiful, talented, _intelligent_ daughter he has.

 

The look on his wife’s face, though, indicates she isn’t quite as enthusiastic about it all. He has a feeling he knows why.

It finally comes up late one night. Riza is curled up into him, head resting gently on his bare chest.

 

“Roy…?” She whispers with an air of hesitancy.

 

“Mmmm...yes, dear?”

 

“Momo...” She swallows, pressing herself closer to him, looking questioningly into his eyes. “What if she wants to learn flame alchemy?”

 

He’s silent as he remembers her words from so long ago.

 

_There can be no more flame alchemists._

 

Roy would be lying if he said he hadn’t at least _thought_ about potentially teaching their daughter. She has a knack for alchemy and a voracious appetite for learning. He has no doubt she’d be able to do it. She is his—no, _their—_ daughter, after all.

 

His lack of response elicits a disappointed hum from his wife. He doesn’t need to say anything—they’ve been together for too long and she already knows what is going through his mind. Riza rolls away from him, shoulders tense as she curls the sheets tightly in front of her chest. The shift in position gives him a clearer look at her back, the secrets of flame alchemy scarred but still vividly present, a dark contrast to her otherwise pale skin. His heart seizes at the memories contained in every line of ink there.

 

Roy rolls over onto his side, propping himself up slightly in hopes of catching a glimpse of his wife’s face.

 

“I won’t teach it to her,” he states, emphatically.

 

She doesn’t budge.“You want to, though.”

 

“I won’t,” He insists, pressing a kiss to the back of her neck as he pushes himself closer to her, wrapping his arms tightly around her waist. She sighs at his touch, relaxing a little. He presses a second one a bit lower on her shoulder, where burn scars meet tattooed array.

 

“I won’t hurt you that way.” _Not again._

**Notes for the Chapter:**

> So this is long overdue! Certain RL circumstances have made it hard for me to write but I've finally got the first part to a point where I feel ok about posting it. I'm trying to keep as many FMA and BNHA characters a part of this as I can and that takes a lot of coordinating I'm not well-equipped for ^^;


End file.
